1. Field of the Invention
The invention relates to a tool for placing or removing joint sockets, for placing or removing joints, and a position-determining device for ascertaining the position of a joint socket of an artificial joint or the position of an artificial joint.
2. Description of the Related Art
Joint sockets that are to be fixed in or on a bone of a recipient without cement generally consist of a metal shell for anchoring in or on the bone and a low-friction insert as counterpart to a complementary joint stem which is spherical in the case of many joints.
A known method of anchoring joint sockets implanted without cement is the clamping thereof in a bone bed that has been specifically prepared having smaller dimensions than the implant. The importance of that method, based on undersizing of the prepared bone bed, can readily be demonstrated using the example of hip socket implants: that method is the most commonly used kind of cementless anchoring of hip socket implants. The next most frequently used method is fixation of the metal socket shell by means of bone screws which are separately positionable. A further kind of cementless anchoring comprises screw-in sockets in which fixation is effected by a thread of large surface area on the outer side of the shell, which thread is screwed into the bone.
Fixation by means of separate bone screws requires corresponding bores in the implant wall, through which the screws are introduced into suitable regions of the pelvis, for example into the roof of the acetabulum. The placement of the screws requires accessibility from different angles and a good view of the operating site.
The known screw-in sockets have a generally coarse, sharp-edged, self-tapping outer thread. The introduction of the implant accordingly requires an opening in the body that needs to be significantly larger than the implant in order to avoid injuries to the surrounding soft tissue structures caused by the sharp-edged, self-tapping thread.
The method of clamping a joint socket or a joint is known as a press-fit anchoring and is suitable particularly for implantation through small openings in the body, because the implants in question do not have projecting, sharp-edged anchoring elements, as in the case of, for example, the screw-in sockets described above. Furthermore, when that method is used, no additional working space is required for insertion of (separate) bone screws.
Depending upon the training of the surgeon and the indication in question, in accordance with the current state of the art joint replacement operations are performed through openings in the body which, after visualization and preparation of the joint parts to undergo surgery, allow secure implantation of the artificial joint components. In the case of customary surgical techniques, openings are created for that purpose in the body that are significantly larger than the artificial joint component. Through those openings in the body, the bone structures for anchoring the artificial joint components are worked on and the latter are finally implanted, with good visual monitoring.
The requirement for a minimum of surgical trauma, which is intended to result in as rapid as possible, pain-reduced rehabilitation of the patient, has led to the development of so-called minimally invasive surgical techniques. Minimally invasive joint implantations are highly desirable, because they offer a number of advantages over conventional operations. The relatively low degree of soft tissue traumatization means shorter wound healing times and accordingly more rapid, less painful rehabilitation of the patient. In addition, fewer functionally important structures are affected by the operation, which has a positive effect on the functionality of the joint provided with implants. Finally, such operations also offer the patient a cosmetic advantage, because a significantly smaller scar is formed.
The implantation of press-fit sockets in the case of conventional non-minimally invasive operations is effected by means of specific impaction instruments or tools, which allow secure implantation with the orientation of the socket being monitored. An example of such an instrument is known from U.S. Pat. No. 5,683,399. That instrument consists of a piece for coupling to the socket shell, a rectilinear rod-shaped intermediate piece for force transmission and a handle with an impact plate, by means of which the impaction force is applied by means of a hammer. It is important in such instruments that impaction with reliable monitoring of the orientation of the implant is ensured. In the case of the instrument according to U.S. Pat. No. 5,683,399, the coupling piece is clamped in the shell by means of a cone connection, the actuation of the cone connection being effected by means of a rectilinear spindle which extends inside the handle and the force-transmitting component.
If such an impaction tool were to be used in a minimally invasive surgical procedure, the surgeon would have a poor view of the operating site because the operating site would be concealed by the tool. Working on the operating site also requires instruments that allow the individual surgical steps to be carried out through a small opening in the body. In addition, surgical access has to be so selected that both joint parts can be implanted through the reduced-size opening in the body. Alternatively, implantations can also be carried out through two different openings in the body, but this is associated with increased risk in the positioning of the individual components, because the two components of a joint, that is to say the joint socket and the joint itself, have to be accurately positioned independently of one another. As can be inferred from what has been said above, particularly in the case of an operation on both joint parts through a reduced-size opening in the body, it is desirable to have a set of instruments that allows manipulation around the soft tissue structures, that is to say avoiding specific soft tissue structures. The implantation tools for the socket and the joint are particularly important in this respect, it being pointed out that no instruments suitable for performing such operations using a minimally invasive procedure are known.